Telephonics RDR-1600, CP-113K, DA-1203A, RT-1601 RT Pilot's Manual

Pilot’s GuideRDR-1600

Color Weather and

Search and Rescue Radar

TM106101 August 2001

Command Systems Division

TM106101(8/01) RDR-1600 Pilot’s Guide

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TABLE OF CONTENTS

PARAGRAPH TITLE

PAGE

1.0 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

2.0 SYSTEM CONFIGURATION . . . . . . . . . . . . . . . . . . .2

2.1 ANTENNA AND RECEIVER-TRANSMITTER . . . . . . .3

2.2 RADAR DISPLAY INDICATOR . . . . . . . . . . . . . . . . . .4

3.0 OPERATIONAL CONTROLS . . . . . . . . . . . . . . . . . . .5

3.1 FUNCTION SELECTOR – CP-113K

CONTROL PANEL . . . . . . . . . . . . . . . . . . . . . . . . .5

3.2 ANTENNA CONTROLS . . . . . . . . . . . . . . . . . . . . . . .6

3.3 DISPLAY CONTROLS . . . . . . . . . . . . . . . . . . . . . . . .6

3.4 PRIMARY MODE SELECTORS . . . . . . . . . . . . . . . . .6

3.5 SECONDARY MODE SELECTOR AND GAIN

CONTROLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

3.6 ALPHANUMERICS . . . . . . . . . . . . . . . . . . . . . . . . . .9

4.0 PREFLIGHT (PFT) . . . . . . . . . . . . . . . . . . . . . . . . . .10

4.1 PREFLIGHT WARNING . . . . . . . . . . . . . . . . . . . . . .10

5.0 THEORY OF OPERATION . . . . . . . . . . . . . . . . . . . .11

5.1 GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

5.2 RADAR PRINCIPLES . . . . . . . . . . . . . . . . . . . . . . .12

5.3 WEATHER RADAR PRINCIPLES . . . . . . . . . . . . . . .13

5.4 RADAR REFLECTIVITY . . . . . . . . . . . . . . . . . . . . . .14

5.5 WEATHER DISPLAY CALIBRATION . . . . . . . . . . . .15

5.6 WEATHER ATTENUATION COMPENSATION . . . . .16

6.0 WEATHER OPERATIONS . . . . . . . . . . . . . . . . . . . .18

6.1 WEATHER MODE – WX . . . . . . . . . . . . . . . . . . . . .18

6.2 WEATHER ALERT MODE – WXA . . . . . . . . . . . . . .19

6.3 TARGET ALERT . . . . . . . . . . . . . . . . . . . . . . . . . . .19

6.4 WEATHER MAPPING AND INTERPRETATION . . . .20

6.5 OBSERVING WEATHER . . . . . . . . . . . . . . . . . . . . .20

6.5.1 Thunderstorms and Turbulence . . . . . . . . . . . . . . . .21

6.5.2 Tornadoes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

6.5.3 Hail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

6.5.4 Icing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24

6.5.5 Snow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24

6.5.6 Lightning and Static Discharges . . . . . . . . . . . . . . . .24

6.5.7 Range Resolution . . . . . . . . . . . . . . . . . . . . . . . . . . .25

6.5.8 Azimuth Resolution . . . . . . . . . . . . . . . . . . . . . . . . .25

6.5.9 Indicator Resolution . . . . . . . . . . . . . . . . . . . . . . . . .26

6.5.10 Short Range Displays . . . . . . . . . . . . . . . . . . . . . . . .27

6.6 PATH PLANNING . . . . . . . . . . . . . . . . . . . . . . . . . . .28

6.6.1 Path Planning Considerations . . . . . . . . . . . . . . . . . .28

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ii RDR-1600 Pilot’s Guide TM106101(8/01)

TABLE OF CONTENTS (CONT.)

PARAGRAPH TITLE PAGE

7.0 SEARCH OPERATIONS . . . . . . . . . . . . . . . . . . . . .31

7.1 GROUND MAPPING . . . . . . . . . . . . . . . . . . . . . . . .31

7.1.1 Looking Angle . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32

7.1.2 Other Aircraft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33

7.2 SEARCH MODE . . . . . . . . . . . . . . . . . . . . . . . . . . .33

7.3 DIFFERENCE BETWEEN WEATHER AND

SEARCH MODES . . . . . . . . . . . . . . . . . . . . . . . . .34

7.4 SEARCH MODES COMPARED . . . . . . . . . . . . . . . .35

7.4.1 Search 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35

7.4.2 Search 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36

7.4.3 Search 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36

8.0 TILT MANAGEMENT . . . . . . . . . . . . . . . . . . . . . . . .37

8.1 TILT CONTROL . . . . . . . . . . . . . . . . . . . . . . . . . . . .37

8.2 TILT PERFORMANCE CHECK . . . . . . . . . . . . . . . .38

8.3 EARLY DETECTION OF ENROUTE WEATHER . . .39

9.0 ANTENNA STABILIZATION . . . . . . . . . . . . . . . . . .40

9.1 LIMITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40

9.2 ERRORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40

9.3 COMPENSATION . . . . . . . . . . . . . . . . . . . . . . . . . .41

10.0 BEACON MODES . . . . . . . . . . . . . . . . . . . . . . . . . .42

10.1 BEACON FORMAT SELECTION . . . . . . . . . . . . . . .43

10.2 DO-172 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43

11.0 AC 90-80 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44

12.0 MULTIPLE INDICATORS . . . . . . . . . . . . . . . . . . . . .45

13.0 SYSTEM SPECIFICATIONS . . . . . . . . . . . . . . . . . .46

13.1 RT-1601 RT UNIT . . . . . . . . . . . . . . . . . . . . . . . . . .46

13.2 DA-1203A ANTENNA DRIVE ASSEMBLY . . . . . . . .46

13.3 CP-113K CONTROL PANEL . . . . . . . . . . . . . . . . . .47

14.0 ADVISORY CIRCULARS . . . . . . . . . . . . . . . . . . . . .48

APPENDIX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .A-1

WARNING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .A-3

CAUTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .A-3

MAXIMUM PERMISSIBLE EXPOSURE

LEVEL (MPEL) . . . . . . . . . . . . . . . . . . . . . . . . . . .A-4

LIST OF ILLUSTRATIONS

FIGURE TITLE

PAGE

2-1 Typical System Block Diagram . . . . . . . . . . . . . . . . . .2

2.1-1 Receiver-Transmitter . . . . . . . . . . . . . . . . . . . . . . . . . .3

2.1-2 DA-1203A Drive Assembly with AA4512A 12”

Flat Plate Antenna . . . . . . . . . . . . . . . . . . . . . . . . . .3

2.1-3 CP-113K Control Panel . . . . . . . . . . . . . . . . . . . . . . . .3

2.2-1 MFD Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

3.1-1 CP-113K Control Panel . . . . . . . . . . . . . . . . . . . . . . . .5

3.2-1 Tilt Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

3.4-1 Primary Mode Selectors . . . . . . . . . . . . . . . . . . . . . . .7

3.5-1 Secondary Mode Selector and Gain Controls . . . . . . .8

3.6-1 MFD Screen Presentations . . . . . . . . . . . . . . . . . . . . .9

4.1-1 Preflight Warnings . . . . . . . . . . . . . . . . . . . . . . . . . . . .10

5.2-1 Radar Transmit-Receive Timing . . . . . . . . . . . . . . . . .12

5.4-1 Reflective Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

5.6-1 STC Electronically Compensates for

Distance Attenuation . . . . . . . . . . . . . . . . . . . . . . . .16

6.1-1 Typical Weather Display . . . . . . . . . . . . . . . . . . . . . . .18

6.3-1 Weather Alert with Target Alert Display . . . . . . . . . . . .19

6.5-1 Storm Components . . . . . . . . . . . . . . . . . . . . . . . . . . .20

6.5.3-1 Finger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

6.5.3-2 Hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

6.5.3-3 Scalloped Edge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

6.5.3-4 U-Shaped . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

6.5.8-1 Azimuth Resolution . . . . . . . . . . . . . . . . . . . . . . . . . . .25

6.5.10-1 Short Range Display . . . . . . . . . . . . . . . . . . . . . . . . . .27

6.6.1-1 Penetration of Weather . . . . . . . . . . . . . . . . . . . . . . . .28

6.6.1-2 Minimizing Doglegging . . . . . . . . . . . . . . . . . . . . . . . .29

6.6.1-3 “Blind Alley” or “Box Canyon” Situations . . . . . . . . . . .29

7.1-1 Over Terrain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31

7.1-2 Over Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31

7.1.1-1 A Smaller Incident Angle . . . . . . . . . . . . . . . . . . . . . . .32

7.1.1-2 Concentration of the Beam . . . . . . . . . . . . . . . . . . . . .32

7.3-1 Wx and SRCH Buttons . . . . . . . . . . . . . . . . . . . . . . . .34

7.4.1-1 Search 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35

7.4.2-1 Search 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36

7.4.3-1 Search 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36

Introduction

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1.0INTRODUCTION

In the early days of aviation, pilots were more concerned with just staying

airborne than worrying about weather. Airplanes were for fun. Pilots flew

only short hops, on clear days, and could often see their destination. There

was little need for navigation equipment. If your compass was working and

your gas held out, you could probably make it home safely. Later, as flying

came of age, thunderstorms and their associated turbulence were more of

a problem. When the weather was good, aircraft utilization was high. But

when storms were prevalent, you might take the long way home.

Today, weather radar is as much at home in the cockpit as the compass.

Corporate aircraft operators, and private pilots, as well as the airlines have

adopted weather radar with full confidence in its usefulness and reliability.

Most commercial airborne weather radars available today also provide the

pilot with one or more ancillary modes of operation and system options that

make the radar more functional and increase its versatility.

Telephonics would like to welcome you to the growing family of Telephonics

Weather Radar System owners and operators.

The RDR-1600 Color Weather Radar System is the newest advancement

of this series of radars. The RDR-1600 series radars are the most popular,

advanced capability, multi-mode radars available from any manufacturer.

The RDR-1600 provides five primary modes of operation: three air-to-

surface search and detection modes, and two conventional weather avoid

-

ance modes. This lightweight digital X-band radar system provides a peak

power of 10 kW, and is primarily designed for fixed or rotary-wing aircraft

engaged in patrol, search and rescue missions, and for transporting

personnel and equipment to remote sites (e.g., off-shore oil rigs, etc.).

The system interfaces with multi-function electronic displays. The MFD is

referred to as an indicator in this manual. The RDR-1600 will also interface

with an Attitude Heading Reference System (AHRS). AHRS Pitch and Roll

data will be converted from digital ARINC 429 to analog pitch and roll data

that is used by the DA-1203A antenna drive unit for antenna stabilization.

The RDR-1600 also has the capability to receive and decode both standard

2-pulse beacon transponders and the DO-172 6-pulse transponders. This

system also provides two short ranges of 0.5 nm and 1.0 nm for search and

rescue.

This manual is designed to help you understand the RDR-1600 and its

operational procedures. Please read it carefully before operating the unit.

If you have any questions, please contact Telephonics (see back cover).

iv RDR-1600 Pilot’s Guide TM106101(8/01)

LIST OF ILLUSTRATIONS (CONT.)

FIGURE TITLE PAGE

8.1-1 Adjusting the Antenna Tilt . . . . . . . . . . . . . . . . . . . . . .37

8.2-1 Altitude vs. Range . . . . . . . . . . . . . . . . . . . . . . . . . . . .38

8.3-1 Weather Target . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39

9.1-1 Aircraft Pitching/Rolling ±30° . . . . . . . . . . . . . . . . . . . .40

10.1-1 Standard Beacon . . . . . . . . . . . . . . . . . . . . . . . . . . . .43

10.2-1 DO-172 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43

14-1 Cross-Section of a Thunderstorm . . . . . . . . . . . . . . . .50

LIST OF TABLES

TABLE TITLE PAGE

5.5-1 Radar Display and Thunderstorm Levels

versus Rainfall Rates . . . . . . . . . . . . . . . . . . . . . . . .15

6.5.9-1 Minimum Distinguishable Target Separation . . . . . . . .26

8.3-1 Antenna Tilt Control Settings . . . . . . . . . . . . . . . . . . . .39

System Configuration (Cont.)

System Configuration

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2.0SYSTEM CONFIGURATION

Figure 2-1.Typical System Block Diagram

2.1ANTENNA AND RECEIVER-TRANSMITTER

The RT-1601 Receiver-Transmitter generates 10 KW pulses of X-band

energy. Reflected signals of weather, search and beacon modes received

by the antenna are amplified and sent to the radar display indicator.

The flat-panel antenna, which is available in diameters of 10, 12 or 18

inches scans 60 or 120 degrees. Swept by a motor-driven gear train, the

vertical component is positioned by the tilt control on the Radar Control

Panel (RCP or CP-113k). A stabilization system presents an upright radar

display while the aircraft is turning, climbing or descending.

Figure 2.1-1.Receiver-

Transmitter

Figure 2.1-2.DA-1203A Drive

Assembly with AA4512A 12” Flat

Plate Antenna

Figure 2.1-3.CP-113K Control Panel

Operational Controls

System Configuration (Cont.)

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2.2RADAR DISPLAY INDICATOR

Figure 2.2-1.MFD Display

The MFD displays green, yellow and red moving maps of weather and
surface features.

The choice of two weather modes, three search modes and antenna scan
of 60 or 120 degrees is selected by the pilot. A target alert feature is active
in the weather alert mode, and a movable track cursor helps the pilot plan
his flight around severe weather. A beacon mode enables the display of
beacon locations and a code feature identifies the beacons. Beacon
Formatting allows for the display of either standard or DO-172 type
beacons. This information can be displayed in any of eight separate ranges.

Rainfall per hour Ground Return Color

0-1 mm No significant return Dark
1-4 mm Light Green
1-12 mm Medium Yellow
12 mm or more Heavy Red

3.0OPERATIONAL CONTROLS

3.1FUNCTION SELECTOR – CP-113K CONTROL PANEL

OFF Removes system power.
STBY System is operationally ready; no display.
TEST

Displays a test pattern without transmitting, identified by

TEST and RT FAULT.
ON System transmits in normal operation.
60°

Directs the antenna to sector scan 60° about the boresight

of the aircraft. This position will work in weather, search

(map), and beacon modes.

Figure 3.1-1.CP-113K Control Panel

Operational Controls (Cont.)

Operational Controls (Cont.)

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BCN

Pressing this button will select the two Beacon type

formats to be selected. Sequentially pressing the Beacon

button will select the following beacon modes:

Beacon Only Mode

Beacon A, Beacon B, Beacon A, Beacon B, . . .

Dual Mode (Beacon/Weather or Beacon/Search)

Beacon A, Beacon B, Beacon Off, Beacon Am . . .

Beacon Only Mode: If the starting mode of operation is

weather (or search), then pressing the beacon button will

place the system in Beacon/Weather (Search) mode. To

activate beacon only mode, press the weather (or search)

button to turn off weather (search) mode. To reactivate dual

mode, press either the weather or search buttons.

Beacon A – Standard 2-pulse beacon

Beacon B – DO-172 compatible beacon

Figure 3.4-1.Primary Mode Selectors

3.2ANTENNA CONTROLS

PULL STAB OFFThis switch is connected to the Tilt Control Knob. When

the Tilt Control Knob is pressed in, the stabilization
function is active. When this knob is pulled out, the
stabilization function is turned off.

TILT Adjusts antenna tilt angle.

Figure 3.2-1.Tilt Control

3.3DISPLAY CONTROLS

The MFD has a brightness control to adjust the brightness of the screen.

3.4PRIMARY MODE SELECTORS

(PUSH ON/PUSH OFF)
Wx Selects weather mode, the primary mode of operation

(automatically selected at turn-on). Weather displayed and
Wx appear on screen. When pressed again, the weather
mode is removed. If no other mode button is active, the Wx
mode remains.

WxA Selects weather alert mode causing red returns to flash if

the MFD is capable of performing this function. WxA
appears and Target Alert is enabled.

SRCH Pressing this push button selects the three Search modes

in sequential cyclic manner (i.e., Search 1, Search 2,
Search 3, Search 1, Search 2, Search 3, etc.). Search
modes are as follows:

Search 1 – Sea clutter rejection. Active on the ten-mile

range or less.

Search 2 – Short range precision mapping. Active on the

ten-mile range or less.
Search 3 – Normal surface mapping.
Beacon mode is compatible with both weather mode and

Search mode.

Operational Controls (Cont.)

Operational Controls (Cont.)

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3.6ALPHANUMERICS

Figure 3.6-1.MFD Screen Presentations

Note

+MFDs display of radar data will vary by manufacturer. Refer to the

MFD Pilot’s Guide for specific radar display.

3.5SECONDARY MODE SELECTOR AND GAIN CONTROLS

BCN GAIN The Beacon Gain is a rotary potentiometer that controls the

gain of the Beacon receiver.

SRCH GAINThe Search Gain is a rotary potentiometer that controls

the gain of the Search receiver.

CODE Pressing this switch selects Beacon Codes in a sequential

cyclic fashion (i.e., Code 0, Code 1, Code 2, . . . Code 15
or Code 0, Code 1, Code 2, . . . Code 9) depending on
Beacon Mode selected. The selected code is annunciated
on the MFD.

When DO-172 Beacon (Beacon Mode B) is selected via
the BCN button, the total of sixteen codes (0-15) can be
selected by the Code switch. Selecting a Standard two­pulse Beacon (Beacon Mode A) via the BCN button, the
total of ten codes (0-9) can be selected by the Code
button. The Code button is not active unless the Beacon
mode has been selected.

Figure 3.5-1.Secondary Mode Selector and Gain Controls

Theory of Operation

Preflight

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5.0THEORY OF OPERATION

5.1GENERAL

The primary use of this radar is to aid the pilot in avoiding thunderstorms

and associated turbulence. Since each operator normally develops unique

operational procedures for use of Weather Radar, the following information

is presented for use at the operator’s discretion.

Operational techniques with the RDR-1600 Series Weather Radars are not

different than with earlier generation radars. The proficient operator

manages his antenna tilt control to achieve the best possible knowledge of

storm height, size, and relative direction of movement.

4.0PREFLIGHT (PFT)

4.1PREFLIGHT WARNING

Test the system to verify proper operation before each flight. Rotate the
function selector from OFF to STBY. Allow system to warm up for about 100
seconds, then move the function selector to TEST. No display appears in
the STBY position and the radar does not transmit in either STBY or TEST.
The test pattern scans 120° and automatically selects the 80 mile range.
Look for distinct color bands and range marks in the order shown. Adjust
display brightness for a comfortable level. Checklist and flight log options
may be used at this time if installed.

WARNING

Do not turn the radar on within 25 feet of ground personnel or
containers holding flammable or explosive material. The radar
should never be operated during refueling.

When ready to use the radar, rotate the function selector to ON position.

Figure 4.1-1.Preflight Warnings

Note

+The design of the system is such that full operation is possible

approximately two minutes after turn-on. Therefore, the pilot may
choose to leave the function switch in OFF, rather than STBY, if no
significant weather is in the immediate area of the aircraft. The life
of the magnetron transmitting tube will be extended by leaving the
system “OFF” when possible. This, in turn, will reduce the cost of
maintenance.

Theory of Operation (Cont.)

Theory of Operation (Cont.)

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5.3WEATHER RADAR PRINCIPLES

Airborne weather avoidance radar, as its name implies, is for avoiding

severe weather – not for penetrating it. Whether to fly into an area of radar

echoes depends on echo intensity, spacing between the echoes, and the

capabilities of both pilot and aircraft. Remember that weather radar detects

only precipitation drops; it does not detect minute cloud droplets. Therefore,

the radar scope provides no assurance of avoiding instrument weather in

clouds and fog. Your indicator may be clear between intense echoes; this

clear area does not necessarily mean you can fly between the storms and

maintain visual sighting of them.

The geometry of the weather radar radiated beam precludes its use for

reliable proximity warning or anti-collision protection. The beam is charac

-

terized as a cone-shaped pencil beam. It is much like that of a flashlight or

spotlight beam. It would be an event of chance, not of certainty, that such a

beam would come upon another aircraft in flight.

WARNING

Weather radar is not practical as a pilot operable collision
avoidance system. Weather analysis and avoidance are the
primary functions of the radar system.

5.2RADAR PRINCIPLES

Radar is fundamentally a distance measuring system using the principle of
radio echoing. The term RADAR is an acronym for Radio Detecting And
Ranging. It is a method for locating targets by using radio waves. The trans­mitter generates microwave energy in the form of pulses. These
pulses are then transferred to the antenna where they are focused into a
beam by the antenna. The radar beam is much like the beam of a flashlight.
The energy is focused and radiated by the antenna in such a way that it is
most intense in the center of the beam with decreasing intensity near the
edge. The same antenna is used for both transmitting and receiving. When
a pulse intercepts a target, the energy is reflected as an echo, or return
signal, back to the antenna. From the antenna, the returned signal is trans­ferred to the receiver and processing circuits located in the receiver
transmitter unit. The echoes or returned signals are displayed on an
indicator.

Radio waves travel at the speed of 300 million meters per second and thus
yield nearly instantaneous information when echoing back. Radar ranging
is a two-way process that requires 12.36 micro-seconds for the radio wave
to travel out and back for each nautical mile of target range. As shown in
the distance illustration in Figure 5.2-1, it takes 123.6 micro-seconds for a
transmitted pulse of radar energy to travel out and back from an area of
precipitation 10 nautical miles away.

Figure 5.2-1.Radar Transmit-Receive Timing

Theory of Operation (Cont.)

Theory of Operation (Cont.)

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5.5WEATHER DISPLAY CALIBRATION

The MFD Radar display should be calibrated to show four levels of target

intensity: Black (level 0), Green (level one), Yellow (level two) and Red

(level three). The meaning of these levels is shown in the following chart as

is their approximate relationship to the Video Integrated Processor (VIP)

intensity levels used by the National Weather Service (NWS). These levels

are valid only when (1) the Wx or WxA modes are selected; (2) the dis

-

played returns are within the STC range of the radar (approximately 40

miles); (3) the returns are beam filling; and (4) there are no intervening

radar returns.

Table 5.5-1.Radar Display and Thunderstorm Levels

versus Rainfall Rates

Video Integrated Processor (VIP)

Categorizations

Rainfall Rate

Rainfall Rate

Display

Level

mm/Hr. In./Hr

Story

Category

VIP

Level

mm/Hr. In./Hr.

Remarks

3

(Red)

12 0.5 Strong 3

Greater
than 12

Greater
than 0.5

Severe turbulence,
possible lightning

2

(Yellow)

4-12 0.17-0.5 Moderate 2 2.5-12 0.1-0.5

Light to moderate
turbulence is
possible with
lightning

1

(Green

1-4 0.04-0.17 Weak 1 0.25-2.5 .01-0.1

Light to moderate
turbulence is
possible with
lightning

0

(Black)

Less

than 1

Less than

0.04

5.4RADAR REFLECTIVITY

What target will reflect the radar’s pulses and thus be displayed on the
indicator?

Only precipitation (or objects more dense than water such as earth or solid
structures) will be detected by an X-band weather radar. Therefore,
weather radar does not detect clouds, thunderstorms or turbulence direct­ly. Instead, it detects precipitation which may be associated with dangerous
thunderstorms and turbulence. The best radar reflectors are raindrops and
wet hail. The larger the raindrop, the better it reflects. Because large drops
in a small concentrated area are characteristic of a severe thunderstorm,
the radar displays the storm as a strong echo. Drop size is the most impor­tant factor in high radar reflectivity. Generally, ice, dry snow and dry hail
have low reflective levels and often will not be displayed by the radar.

A cloud that contains only small raindrops, such a fog or drizzle, will not pro­duce a measurable radar echo. But if the conditions should change and the
cloud begins to produce rain, it will be displayed on radar.

Figure 5.4-1.Reflective Levels

Theory of Operation (Cont.)

Theory of Operation (Cont.)

16 RDR-1600 Pilot’s Guide TM106101(8/01) TM106101(8/01) RDR-1600 Pilot’s Guide

17

Attenuation due to precipitation is far more intense and is less predictable

than attenuation due to distance. As the radar pulses pass through mois

-

ture, some radar energy is reflected, however, much of that energy is

absorbed. If the rain is very heavy or extends for many miles, the beam may

not reach completely through the area of precipitation. The weather radar

has no way of knowing if the beam has been fully attenuated or has

reached the far side of the precipitation area. If the beam has been fully

attenuated, the radar will display a “radar shadow” which appears as an end

to the precipitation when, in fact, the heavy rain may extend for many more

miles. In the worst case, precipitation attenuation may cause the area of

heaviest precipitation to be displayed as the thinnest area of heavy precip

-

itation. Or it may cause one cell containing heavy precipitation to totally

block or shadow a second heavy cell located behind the first cell and pre

-

vent it from being displayed on the radar.

CAUTION

Never fly into radar shadows and never believe that the full extent of
heavy rain is being seen on radar unless another cell or a ground
target can be seen beyond the heavy cell.

Proper use of the antenna tilt control can help detect radar shadows.

Attenuation can also be a problem when flying in a large area of general

rain. If the rain is moderate, the radar beam may only reach 20 or 30 miles

before it is fully attenuated. The pilot may fly along for many miles seeing

the same 20-30 miles of precipitation ahead on the radar when, actually, the

rain may extend for a great distance. In order to aid in reducing the effects

of precipitation attenuation, the RDR-1600 contains sophisticated weather

attenuation compensation circuitry. The Attenuation Compensation feature

is totally automatic and requires no pilot action to activate it. However, the

Compensation logic cannot operate until echoes are within the Sensitivity

Time Control range of approximately 40 miles. Whenever a level two

level (yellow) or level three (red) echo is displayed within the STC range,

the Compensation circuits cause the receiver gain to increase while the

antenna scans the sector containing heavy rain. The Compensation circuit

-

ry allows the radar beam to effectively look deeper into and through heavy

rain to search for possible storm cells beyond. While Attenuation

Compensation does not eliminate precipitation attenuation, it does allow the

radar to see through more rain at short ranges where every bit of weather

information possible is needed. If there is suspicion that the radar is atten

-

uating due to precipitation, exercise extreme caution and ask the ATC

Controller what they are showing. Often the ground-based ATC radar will

have a better overall picture of a large rain area and the pilot can compare

the controller’s information with his own radar picture to avoid the strongest

cells in a general area of rain.

5.6WEATHER ATTENUATION COMPENSATION

Attenuation is an extremely important phenomenon for the weather radar
operator to understand. When a radar pulse is transmitted into the
atmosphere, it is progressively absorbed and scattered so that it loses its
ability to return to the antenna. This attenuation or weakening of the radar
pulse is caused by two primary sources, distance and precipitation. The
RDR-1600 radars have several advanced features which significantly
reduce the affects of attenuation but no airborne weather radar can elimi­nate them completely. It is therefore up to the operator to understand the
radar’s limitations in dealing with attenuation.

Attenuation because of distance is due to the fact that the radar energy
leaving the antenna is inversely proportional to the square of the distance.
For example, the reflected radar energy from a target 60 miles away will be
one fourth (if the target is beam filling) of the reflected energy from an
equivalent target 30 miles away. The displayed effect to the operator is that
as the storm is approached it will appear to be gaining in intensity. To com­pensate for distance attenuation, both Sensitivity Timing Control (STC) and
Extended STC circuitry are employed. The RDR-1600 has an STC range of
approximately 40 nautical miles and within this range the radar will elec­tronically compensate for the effects of distance attenuation with the net
effect that targets do not appear to grow larger as the distance decreases.

Outside the STC range the Extended STC circuitry increases the displayed
intensity to more accurately represent storm intensity. The Extended STC
will not, however, totally compensate for distance attenuation and,
therefore, targets in this range can be expected to grow as the distance
decreases until reaching the STC range.

Figure 5.6-1.STC Electronically Compensates for

Distance Attenuation